78' SC CIS richens as rpm's build?

bobswei · bobswei's Garage

I'm trying to smog a 78' SC that originally was too rich on CO%. (5.30% at 2500 rpm). Idle CO was around 4.80. I was able to have use of a local smog shops analyzer to adjust and got the idle CO to around 0.20% but then when rpm's go to 2500 on the rollers, CO goes to rich, I believe close to 4.0%. Turning richness down more starts causing a lean misfire. I'm not really "emission savvy". So, what would cause the richness to go up in disproportion to the rpm's? Air pump related maybe?
Thanks for any suggestions. Bob

timmy2 · timmy2's Garage

Advance mechanism in distributor not operating properly to advance timing for a clean burn?

bobswei · bobswei's Garage

I took the cap off and the advance mechanism seems OK. Also, the car has tons of power over 4K rpms's. Could there be more than one adjustment on the CIS?
Thanks for the response.

tcar · 08-20-2014, 07:04 PM

Quote:

Originally Posted by bobswei

I'm trying to smog a 78' SC that originally was too rich

78 feet is too long for an SC, man, that's the problem...

What year?

timmy2 · timmy2's Garage

Tell them the factory spec for CO at idle when the car is fully warm is 2.5 +/- 1,0 and the car was not designed to meet their new specs.

Sent from my iPhone using Tapatalk

The cap'n · 08-21-2014, 05:43 AM

Quote:

Originally Posted by tcar

78 feet is too long for an SC, man, that's the problem...

What year?

And I thought I was mean!

Timing isn't likely to be an issue because the engine's burning pretty clean. Look at the HCs. First thing I would look at is the control pressure regulator, a.k.a. the warmup regulator. A failed CPR would make the thing rich all the time, and you couldn't adjust that away. At this point, if it's been running like that for a long time, the catalyst is probably toast.

The Cap'n

javadog · 08-21-2014, 05:58 AM

First thing I'd check is whether or not it has all the correct CIS components on it. Quite a few cars have been "repaired" with the wrong WUR, fuel head, etc.

Then I'd check the fuel pressures and for air leaks.

Then I'd see if the cat was doing anything. A '78 used a 2-way cat, which isn't going to do as much as a later 3-way cat, even on a good day.

I'd also argue that their CO spec is wrong. Porsche only specified a CO spec for idle, and a specific way to measure it. Who knows what the CO was on a properly tuned '78 SC at other engine speeds?

JR

The cap'n · 08-21-2014, 06:57 AM

Ignition isn't gonna affect the CO, for the most part. CO is a reflection of the air/fuel mixture. It is what the CPR/fuel distributor says it is. Ignition affects the burning of the mixture, which is reflected in this case by the HC number (which are well within specs).

I agree, a 3 way cat (which is the only replacement cat approved for sale in CA) is MUCH better, but it doesn't address the fundamental mixture problem. Besides, the cat primarily addresses HCs, and it appears to be working to some extent. (I may have mis-spoken in my earlier condemnation of the cat, but it still could be bad.) Your point about misappropriated fuel system components is valid. Lotsa cars out there running a hodge-podge of mismatched components.

While there may be some argument for the original base idle CO specification, the currently prescribed limits are easily achieved by a properly equipped '78 911 with everything functioning as it should, and the guy at the smog station has no leeway on the specs. Even with the air pump out of the equation, 5+% is WAY too high (and it should drop significantly at higher RPM, not rise). While failing the test is always a concern, if the test was completed the car is now branded a "gross polluter", and has to go to a test only station. Again, they have no say on the specs. The owner might take it to a referee, but I'm sure the specs question is not gonna fly with him, either.. Another part of the bad news is the car now has to be smogged at a test only station every year.

The Cap'n

RarlyL8 · RarlyL8's Garage

+1 on the advice of others 5% is high enough to smell it.
Can we assume the engine has a fresh tune up?
Cat in good shape?
If so and the engine idles well at 0.2% CO it would indicate an idle/cruise transition issue. '78 has no Lambda so control is purely mechanical (WUR). How old are the fuel head and regulator?

bobswei · bobswei's Garage

OK, lots of great ideas in here. I owned an SC in the past but it's been a few years. All components look identical and I remember making an adjustable WUR for it. Simple idea of a screw that you tap in with a hammer and had a wing nut to turn to back it back out for adjusting. But, you make me think that once the car is warmed up, disconnect the WUR and then it wont over enrich the mixture (if that is the cause)? I've had the car for a few months and it had been sitting for years since it had a salvage title due to front damage. I checked the BAR website and last time it was smogged was, I believe around 10 years ago and it passed. Didn't see any fails. Also, not sure how to check for air leaks or what to check. Thanks for the responses.
Here's some pix of what is there:

bobswei · bobswei's Garage

...I forgot. According to the smog tech., the cat is "good". Also, I'm in California's beautiful Bay Area. If anyone needs a great smog guy in Fairfield, that's on your side, IM me.

ossiblue · 08-21-2014, 03:22 PM

Quote:

Originally Posted by bobswei

OK, lots of great ideas in here. I owned an SC in the past but it's been a few years. All components look identical and I remember making an adjustable WUR for it. Simple idea of a screw that you tap in with a hammer and had a wing nut to turn to back it back out for adjusting. But, you make me think that once the car is warmed up, disconnect the WUR and then it wont over enrich the mixture (if that is the cause)? I've had the car for a few months and it had been sitting for years since it had a salvage title due to front damage. I checked the BAR website and last time it was smogged was, I believe around 10 years ago and it passed. Didn't see any fails. Also, not sure how to check for air leaks or what to check.

If the WUR is working properly, disconnecting it will not help. A warm WUR is designed to lean the mixture, not richen it. The WUR does provide for enrichment during wide open throttle, but that should not be kicking in at 2500 rpm as it's activated by vacuum from the throttle body.

javadog · 08-21-2014, 03:32 PM

You can't disconnect a WUR...

Okay, your main problem is probably the fact that your engine sat for 10 years. Some of the CIS components don't like that and they seldom wake up from such a slumber and work like they are supposed to. My advice...

If you want to see what you have, compare the Bosch part numbers on each of the major components with those that are suppposed to be on that engine type, whatever it may be. The photos you posted aren't enough.

Then, give the car to a shop that can troubleshoot a CIS system and let them sort it out. Otherwise, you'll still be tinkering with this thing next winter.

JR